Coronary artery disease is a leading cause of death in the United States today, and involves the accumulation of atherosclerotic plaque in the coronary arteries, resulting in ischemia of the heart. The disease, which is manifested as chest pain or angina, afflicts several million people in the United States.
A surgical method that has been used to treat this disease for more than thirty years is coronary artery bypass grafting (CABG), in which the patient's chest is opened and an obstructed artery replaced with a native artery harvested elsewhere or a synthetic graft. Such surgery creates significant trauma to the patient, requires long recuperation times, and poses serious risks of mortality. In addition, experience has shown that the bypass vessel or graft becomes obstructed with time, requiring further surgery.
More recently, minimally-invasive catheter-based therapies have been developed, such as percutaneous transluminal coronary angioplasty (PTCA). In PTCA, a mechanical dilatation device, generally a balloon catheter, is disposed across an obstruction in the patient's artery and then dilated to compress the plaque lining the artery to restore patency to the vessel. More recently, endoluminal prostheses, commonly called "stents," are deployed in the artery following the angioplasty procedure to retain the patency of the vessel.
Balloon dilatation devices generally employ either minimally-compliant balloons, which experience a relatively small increase in diameter when the balloon is expanded, or compliant balloons, which experience a relatively large increase in diameter in response to an increase in pressure, as described, for example, in U.S. Pat. No. 5,447,497 to Sogard et al. Non-compliant balloons are generally favored for angioplasty because they may be reliably expanded to a known size, whereas compliant balloons permit treatment over a larger range of diameters. In order to provide a mixture of the desirable characteristics of each of these types of balloons, dilatation devices have been designed, as described in U.S. Pat. No. 5,447,497, that include layers of both compliant and non-compliant material.
Other balloon dilatation devices have employed elastomer impregnated braided material or nets to constrain the inflated size of the device, such as described in U.S. Pat. No. 4,702,252 to Brooks et al. and U.S. Pat. No. 4,108,236 to Ochiai et al. Still other devices, such as described in U.S. Pat. No. 4,998,539 to Delsanti and U.S. Pat. No. 5,221,261 to Termin et al. include members for supporting a vessel following angioplasty. U.S. Pat. No. 4,998,539 describes a separately movable plaited net disposed over a balloon catheter. The plaited net is expanded against the interior of the vessel by the balloon during angioplasty, and temporarily remains in place after balloon deflation to prevent detachment of material from the vessel wall.
One disadvantage encountered in PTCA has been the inability to dilate certain types of stenosis without exceeding the limitations imposed on the balloon element by materials considerations. For example, most angioplasty catheters constructed from polyethylterephalate (PET) or polyethylene (both non-compliant materials), generally may not be pressurized above 22 atmospheres without risk of rupture. Rupture of the balloon element often may have fatal consequences, because it may cause dissection of the vessel and require an emergency thoracotomy to repair the dissected vessel.
Accordingly, if a stenosis cannot be disrupted using dilatation element pressures within the useful range of the dilatation element material, then the constriction must be addressed by other means, such as conventional bypass or grafting procedures.
A further drawback to previously known balloon dilatation devices is the relative small range of expanded diameters that such devices can achieve. For example, high pressure balloon catheters commercially available today generally have expanded diameters no exceeding 12 mm. Accordingly, such devices cannot generally be used in larger diameter vessels, such as the pulmonary artery, aorta, or hollow-body organs, because at larger diameters the balloons tend to bulge locally and lose their strength, facilitating rupture.
In view of the shortcomings of previously known dilatation devices, it would be desirable to provide apparatus and methods for dilating a vessel that permit dilatation of certain hardened stenoses using higher pressures than heretofore attainable.
It also would be desirable to provide apparatus and methods for dilating vessels using balloon elements that allow the use of higher pressures than available in previously known devices, and that reduce the risk of vessel dissection resulting from balloon rupture.
It further would be desirable to provide apparatus and methods of dilating large diameter vessels having diameters from 15 to 35 mm, such as the aorta and pulmonary artery, but which apparatus are less prone to localized bulging, thereby reducing the risk of rupture.